JP3510900B2 - Method and apparatus for forming blown film - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a blown film molding method, which has a small melt tension, and therefore has a bubble shape of a so-called long neck type (a bubble shape in which the position of expansion of the bubble is far away from the die). It was considered difficult to obtain a linear low density polyethylene (hereinafter referred to as LLDPE), low density polyethylene (hereinafter referred to as LDPE) or high density polyethylene (hereinafter referred to as HDPE), ethylene-vinyl acetate copolymer. Long-neck type inflation film that can be molded even with an ethylene-based copolymer such as an ethylene-acrylate-based monomer copolymer, or a synthetic resin such as polypropylene, polyamide, or polyester to obtain a strong film. Moldable, haze, gloss, clari Optical properties such as I over relates to a film forming method and a molding apparatus for producing a high productivity excellent thermoplastic resin film strength.

[0002]

2. Description of the Related Art There have been many proposals for producing blown film by air-cooling method, and the shapes of resin bubbles for forming a film by these proposals can be roughly classified into four types (see FIGS. 1 and 4). ~ Fig. 5).

Factors that determine the shape of the molten resin bubble include cooling capacity, film take-up speed, molten resin temperature, etc., and linear polyethylene such as ultra high molecular weight high density polyethylene (hereinafter referred to as HMWHDPE). With polyethylene having a high melt tension, so-called long-neck type bubble film formation is often adopted, and it is supplied in large quantities in the field of shopping bags and the like as a high-strength balance film.

However, in this method, the molten bubble is gradually cooled, so that a transparent film cannot be obtained.

On the other hand, the LLDPE currently on the market has a relatively small melt tension, its flow characteristics are significantly different from those of HMWHDPE, the stability of the bubbles is poor, and it is difficult to form the bubbles into a shape such as a long neck type. Yes,
Usually, the bubble shape of the type of FIG. 4 or the type of FIG. 5 (referred to as low frost line type) or T-
It is formed by the die method. The same applies to other thermoplastic resins having a small melt tension.

In the production of the blown film by this low frost line type, the molten bubble is rapidly cooled to obtain a transparent film, but the biggest problem with this method is that the stability of the bubble is poor at high-speed production and the bubble is not produced. The thickness and width of the film tend to fluctuate due to shaking, and when the film is produced at high speed, the orientation in the take-up direction becomes stronger and the strength in the machine direction increases. The strength in the direction (transverse direction) is remarkably lost, and therefore the balance of strength is lost and it is easy to tear in the vertical direction, so that it is difficult to increase the take-up speed, and the productivity is limited.

In order to form a film of synthetic resin having a small melt tension by the inflation method,
There was no choice but to adopt a low frost line type bubble shape capable of stable production even at a low speed, or to adopt production by the T-die method.

[0008]

DISCLOSURE OF THE INVENTION In the present invention, when a film of a thermoplastic resin is produced by an air-cooled inflation method, even if a thermoplastic resin having a low melt tension is used, there is a fear of a molten resin bubble due to molding by a long neck type. The goal was to eliminate the qualitative effects, stabilize the bubble, and establish a film forming method with excellent optical properties such as haze, gloss, and clarity.

[0009]

SUMMARY OF THE INVENTION The present invention is a polyethylene
Copolymers of ethylene and radically polymerizable monomers,
Low melt tension consisting of propylene or mixtures thereof
If the temperature of the extruded resin is the melting point of the thermoplastic resin,
40 ° C above the melting point and 120 ° C above the melting point
The air intake at the base and air out at the top.
Equipped with a mouth, the ratio of internal stabilizer diameter / die diameter is 0.7
The molten resin bubble is made to flow inside by continuously flowing a small amount of air between the internal stabilizer of 1.0 to 1.0 and the molten resin bubble.
While supporting the stabilizer in a non-contact state, the molten resin bubble is cooled by blowing cooling air from the air ring having a plurality of annular slits provided at a position where the molten resin bubble is rapidly expanded, in the direction of taking the bubble. At the same time, the molten resin bubble temperature at the air ring outlet is adjusted to a range of a crystallization temperature of the thermoplastic resin and a temperature 60 ° C. higher than the crystallization temperature of the resin, and the expansion ratio (bubble diameter after expansion / rapid
Bubble diameter at the narrowest point before expansion) 1.3
~ 6.0, distance from die surface to frost line is 4
A method for molding an inflation film, which comprises molding in the range of 0 to 2000 mm . The above-mentioned object was achieved by developing.

As a device for forming the above-mentioned blown film, a thermoplastic resin comprising an extruder, an annular die for inflation provided with a bubble internal stabilizer, and an air ring. Inflation film molding equipment has an air inlet at the base and an air outlet at the top.
The internal stabilizer diameter / die diameter ratio is 0.7-1.
0 small as the molten resin bubble internal regulated body does not contact the
A device for continuously flowing a certain amount of air and a plurality of annular slits at positions where the molten resin bubbles are rapidly expanded, and a single air ring that blows out cooling air in the take-up direction of the molten resin bubbles by the annular slits. It was confirmed that the above-mentioned inflation film molding can be easily carried out by developing an inflation film molding apparatus including the above.

[0011] As the thermoplastic resin to which the present invention, positive Riechiren; copolymers et styrene and a radical polymerizable monomer; polypropylene comma others be mentioned small thermoplastic resin melt tension such as mixtures thereof You can
However, a polymer having a high melt tension as much as possible has a better bubble stability.

Even LLDPE has good bubble stability during molding, and therefore, it is generally possible to take it off at a higher speed than the low frost line method, and the film molded by the method of the present invention is excellent in transparency and strength. The transparency is comparable to that of casting polypropylene film and can be used as an inexpensive film that can be used at low temperature.

In the following description, LLDP is used as the thermoplastic resin.
Taking E as a representative, description will be made with reference to the drawings. The inflation molding method usable in the present invention may be either upward blow or downward blow.

The extruding temperature of the resin is relatively low because there is no air ring 5 close to the die 1, and the extruding temperature of the resin slightly changes depending on the kind of the resin, but is higher than the melting point by 40 ° C.
Within a temperature range of 120 ° C higher than the melting point, preferably the melting point +
It is within the range of 40 ° C to the melting point + 80 ° C. For example, LLDP
If it is E, it is preferable to mold in the temperature range of 170 to 210 ° C. If the temperature is lower than 170 ° C., melt fracture tends to occur, and if the temperature is higher than 210 ° C., the melt tension becomes small and the stability of the bubble 3 is easily impaired.

In this case, since LLDPE or a resin composition containing it has a property of easily causing melt fracture at a low extrusion temperature, the lip gap of the die 1 is 2.0 to 10.0 mm (preferably 2. 5-5.5
mm) and that of HDPE, or a bubble heater (not shown) for heating the surface of the molten resin bubble 3 is provided between the die 1 and the air ring 5 (on the die side from the expansion point). By taking the above means, it is possible to avoid roughening of the surface. As the lip gap becomes larger than 7.0mm, the uniformity of the film thickness is lost, so even if the melt fracture can be made smaller, it should not be made larger than 10.0mm and the bubble heater avoids the rough surface. Preferably.

The molten resin bubble 3 extruded at a relatively low temperature supports the inner surface of the molten resin bubble 3 in a non-contact state with the stabilizer 4 and takes it out. In this case, it is also a good method to provide the stabilizer 4 on the die side of a normal internal stabilizer with an outlet stabilizer B having a slit diameter substantially the same as or slightly larger than the slit diameter of a die coaxially supported with the stabilizer. The outlet stabilizer B may be composed of a plate, a net, a spring or the like in order to minimize the contact resistance. This is effective because the bubble shape of the bubble 3 is retained by the outlet stabilizer B, and this portion is further stabilized. The molten resin bubble 3 is taken and rapidly expanded while being supported by the internal stabilizer 4.

In order to support a bubble in a non-contact state with the internal stabilizer 4 having an air layer on its surface, a small amount of air is continuously supplied between the internal stabilizer and the bubble, usually in the same direction as the bubble is drawn. It can be achieved by flowing in the direction. For example,
An air inlet 6 is provided at the base of the internal stabilizer 4, an air outlet 7 is provided at the top of the internal stabilizer, and air is allowed to flow so that the internal pressure of the molten resin bubble 3 can be adjusted to be constant. The body 4 can be supported in a non-contact state. In this case, the surface of the internal stabilizer should be as smooth as possible and the turbulence of the air flow should be minimized.

The diameter of the internal stabilizer is not particularly limited,
Although it may be thicker than the diameter of the die, it is thinner than the exit stabilizer, and usually, it is preferably 0.7 to 1.0 with respect to the diameter of the die. This makes it possible to obtain a large substantial expansion ratio (ratio of bubble diameter after expansion / bubble diameter before rapid expansion) even when films of the same size are manufactured using the same size die. Conversely, it shows that there is a merit that a film having the same expansion ratio can be produced by using a film having the same size and a die having a larger diameter.

Increasing this substantial expansion ratio has the effect of increasing the strength in the lateral direction (the direction perpendicular to the film take-up direction) and increasing the impact strength. It is good to set it as the range of -6.0, and preferably set it as the range of 1.5-4.5.

The film obtained when the substantial expansion ratio is lower than this tends to cause longitudinal tearing and has a low impact strength. On the other hand, if the substantial expansion ratio is 6.0 or more,
It should be avoided because the orientation in the lateral direction is too strong and the film is easily broken, which easily causes breakage of bubbles during production.

In the production of the blown film of the present invention, the molten resin bubble 3 is supported by the internal stabilizer 4 through the air layer, so that the contact resistance here is extremely small and therefore the thermoplastic resin bubble having a small melt tension. Even then, stable high-speed pickup is possible.

The molten resin bubble temperature is one of the important requirements in the present invention. The molten resin bubble 3 extruded from the die 1 at a relatively low temperature needs to be at the crystallization temperature of the resin used at the air ring outlet and in a temperature range higher than the crystallization temperature by 60 ° C., preferably crystallization temperature +10. It is a temperature range of ℃ ~ crystallization temperature + 40 ℃. When the temperature is lower than the crystallization temperature, not only the melt bubble gradually cools and the transparency decreases, but also the expansion becomes impossible or incomplete, and the dispersion becomes large, and the target thickness and size are reduced. I can't get a film. Further, when the temperature is higher than this temperature range, the expansion of the molten resin bubble 3 becomes non-uniform, or the stability of the bubble is impaired, which makes it difficult to produce a film having uniformity (generally, a thermoplastic resin). The crystallization temperature at is about 10 ° C. lower than the melting point of the resin).

For example, in the case of linear low-density polyethylene, the resin temperature at the air ring outlet must be in the range of the melting point of the thermoplastic resin to 180 ° C. The molten resin bubble expands sufficiently in the air ring, or expands immediately after exiting the air ring to form a film with a predetermined thickness and size, but when high transparency is required, the film The thickness is preferably 50 μm or less, more preferably 40 μm or less. According film thickness becomes thicker, which inevitably opacifying for the slow cooling. By using a bubble heater as a countermeasure, this problem can be solved to a considerable extent.

The outlets (52, 53, 54) of the plurality of annular slits of the air ring 5 having the outlets having the concentric annular slits for blowing out two or more cooling air are blown out in the outward direction of the bubble diameter. However, it is preferable to form air so as to blow out the air substantially in parallel with the bubble taking-in direction, as shown in FIG. 2 or FIG.

Annular slits (52, 5) of the air ring 5
3, 54), the depressurized atmosphere created by the blowing of the cooling air in the bubble take-up direction affects the molten resin bubble, and the bubble suddenly expands at this position.

Although the cooling air outlets (52, 53, 54) of the air ring 5 are shown in FIG. 2 or 3 as triple annular slits, they may be double or more. The upper end wall surface of the air outlet of each of the air outlets 52, 53, 54 may be inclined to increase the degree of pressure reduction. A cover 55 may be attached to the tip of the air ring also for the purpose of blocking the flow of external air and the reduced pressure atmosphere from the outside.

Therefore, the position of the frost line 8 which affects the properties of the obtained film can be freely changed by moving the position of the air ring 5. Air ring 5
The position of is usually required to be separated from the die surface by 50 mm or more, preferably 100 mm or more, and more preferably 200 mm or more.
It is better to separate them by mm or more. If it is too close to the die surface, the cooling effect will decrease.

Further, as the air ring 5, in order to accelerate the cooling of the molten resin bubble 3, cooling air (a plurality of annular slits) outlets (52, 53, 5) in the bubble taking direction are provided.
In addition to 4), it is also effective to use an air ring (see FIG. 3) having an outlet 57 for the purpose of cooling in the opposite direction (molten resin bubble from the die to the air ring). According to this method, the temperature of the extruded resin can be raised, albeit a little, so that the operating conditions can be somewhat relaxed and the productivity can be increased. The outlet 57 in the opposite direction is not limited, but can be blown to the molten resin bubble at an angle of about 45 ° to 60 °.

When the molten resin bubble 3 expands rapidly, the resin film becomes thin and is rapidly cooled, and after solidification, air is squeezed by a nip roll (not shown) like a normal inflation and taken up by a winding machine. Becomes

[0030]

Function The present invention is an ordinary HMWHD for balance film.
This is an effective manufacturing method not only for a thermoplastic resin having a high melt tension such as PE but also for a thermoplastic resin that has a low melt tension and is difficult to be inflation-molded by a long neck type.

The reason why the film obtained by the method of the present invention has high transparency is considered as follows.

It is well known that, in general, a molten resin bubble extruded from a die swells at the outlet due to the swell effect, and the outer diameter of the molten resin bubble becomes several percent to several dozen percent larger than the diameter of the die.

When swelling due to swell, the surface of the bubble shows a large unevenness. When the film is formed in the low frost line type bubble shape shown in FIG. 4 or 5, the film surface is rapidly expanded, so that the film surface is strongly affected by the swell effect.

However, in the case of the long neck type, the molten resin bubble slowly moves to the expansion point, during which the surface irregularities generated by the swell are greatly relaxed, and the relaxed bubble expands rapidly. It is estimated that the effect of swell can be greatly reduced, which is one of the reasons for obtaining a film having a smoother surface.

For example, haze is one of the indexes of the transparency of the film, but it is known that most of the haze of the film is in external haze (opacity due to non-transmission of light due to unevenness of the film surface). ing.

It is considered that the high transparency of the film of the present invention is obtained by using a long neck type part of which has a moderate swell effect.

When the neck point (point immediately before the rapid expansion) is lowered to the crystallization temperature, crystals grow and haze deteriorates. In the present invention, however, this problem is caused by regulating the temperature of the air ring outlet. Is also avoided, which is considered to be one of the reasons for obtaining a highly transparent film.

In the molding method of the present invention, the reason could not be clarified, but the molten resin bubble temperature at the outlet of the air ring 5 was regulated, and melting was carried out by the reduced pressure atmosphere accompanying the cooling air blowing from the plurality of annular slits of the air ring. It is presumed that, by adopting the method of rapidly expanding the resin bubbles, inflation molding could be performed without problems not only for resins with high melt tension but also for low melt tension.

Particularly , by supporting the stabilizer in a non-contact state, the molten resin bubble is stabilized, and due to synergistic effects such as rapid cooling of the molten resin due to rapid expansion, optical properties such as haze, gloss and clarity are remarkably increased. It seems to have been improved.

[0040]

【Example】

(Example 1) Density 0.923 g / cm ³ , JIS K-
Melt flow (hereinafter referred to as MFR) according to condition 4 in Table 1 of 7210, 1.0 g / 10 min of linear polyethylene was used with an inflation film molding apparatus equipped with a die having a lip gap of 3 mm and a diameter of 100 mmφ, and a resin temperature of 2.
Extruded at 00 ° C. As the stabilizer, a cylinder with a diameter of 100 mmφ, whose surface is coated with Teflon, is used to support a molten resin bubble in a non-contact state while supplying a small amount of air from the base of the stabilizer, and a film with a folding width of 314 mm and a thickness of 30 μm is taken out. It was molded at a speed of 50 m / min. The molten resin bubble had a temperature of 130 ° C. at the outlet of the air ring composed of double annular slits. Frost line is 6 from the die side
50 mm, frost line temperature is 111 ° C. The evaluation of the obtained film is shown in Table 1.

The temperature at the outlet of the air ring was measured with a model IR-AP thermometer manufactured by Chino Co., Ltd. at a distance of 150 c.
m, measurement area; the diameter was 45 mm, and the portion closest to the air ring was measured. Haze, gloss and clarity are J
It was measured by the method of IS K-7105.

(Examples 2 and 3) Density 0.923 g / cm
³ , MFR 1.0 g / 10 min LLDPE 80% by weight, density 0.925 g / cm ³ , MFR 0.8 g / 1
Using a resin composition composed of 20% by weight of LDPE for 0 minutes,
Using the same apparatus as in Example 1, the conditions were changed to form a film. The evaluation of the obtained film is shown in Table 1.

(Example 4) In the film molding of Example 2, the take-up speed was 30 m / min, and an infrared heater (bubble heater) of 3.0 kw was provided between the die and the air ring to improve transparency. . The evaluation of the obtained film is shown in Table 1. Transparency (haze, gloss, clarity) shows a significant improvement.

Example 5 Density 0.953 g / cm ³ ,
MFR 0.5 g / 10 min HDPE60 wt%, density ^{0.925g / cm 3, MFR 0.8g /} 10 min L
Example 1 using a resin composition consisting of 40% by weight of DPE
Using the same apparatus as above, a film was formed under the conditions shown in Table 1 at a resin temperature of 200 ° C. The evaluation of the obtained film is shown in Table 1.

(Comparative Example 1) Using the same resin and apparatus as in Example 2, a film was formed under the conditions shown in Table 1.
The optical properties such as haze, gloss and clarity of the obtained film were remarkably deteriorated.

(Comparative Examples 2 to 4) Inflation film molding of low frost line type (bubble shape as shown in FIG. 3 or 5) in which molten resin bubbles immediately expand from the die outlet is formed with the same resin as in Example 2. went. The evaluation of the obtained film is shown in Table 1.

In Comparative Examples 2 to 3, the decrease in transparency was slight, but even when the frost line was set to be almost the same as in Example 1 as in Comparative Example 3, the mechanical properties of the obtained film were Remarkably decreased. In Comparative Example 4, when the take-up speed was set to 50 m / min with the same bubble shape, the molten resin bubble became unstable and frequent cutting occurred, making molding impossible.

[0048]

[Table 1]

[0049]

INDUSTRIAL APPLICABILITY The present invention provides an outlet for an air ring having a plurality of annular slits which are supported in a non-contact state with a stabilizer and are provided at positions where they are rapidly expanded when forming a film of a thermoplastic resin by an inflation method. Temperature of the thermoplastic resin is 60 ° C. from the crystallization temperature of the thermoplastic resin.
When forming a film with a long neck type by adjusting to a high temperature range, the molten resin bubble is stable even if it is a thermoplastic resin with a small melt tension such as LLDPE, and optical characteristics (haze, gloss, clarity) It has been found that excellent film can be stably produced.

The molding apparatus used for this purpose can be preferably used in the above-mentioned blown film molding method.

Further, it has been found that even a thermoplastic synthetic resin which easily causes melt fracture can be greatly improved in haze, gloss and clarity by providing a bubble heater between the die and the air ring for production.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing an example of a blown film molding method according to the present invention.

FIG. 2 is a sectional view showing an example of an air ring used in the present invention.

FIG. 3 is a cross-sectional view showing another example of an air ring.

FIG. 4 is a conceptual diagram of an example of a conventional blown film molding method using a low frost line type.

FIG. 5 is a conceptual diagram of another example of the conventional blown film molding method using a low frost line.

[Explanation of symbols]

1 die 3 molten resin bubbles 4 Stabilizer 5 Air ring 51 air passage 52 Outlet 53 Outlet 54 Outlet 55 cover 56 air passage 57 Air outlet 8 Frost line B exit stabilizer

─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Takeshi Onoda 3-2 Chidori-cho, Kawasaki-ku, Kawasaki City, Kanagawa Prefecture Showa Denko K.K. 2 Showa Denko KK Kawasaki Plastics Research Laboratory (56) Reference JP-A-2-34324 (JP, A) JP-A-46-5744 (JP, A) JP-A-49-61252 (JP, A) JP-A-SHO 53-42254 (JP, A) JP-A-53-75266 (JP, A) JP-A-54-93057 (JP, A) JP-A-57-34920 (JP, A) JP-A-58-119824 (JP, A) JP 58-191126 (JP, A) JP 58-219021 (JP, A) JP 59-42931 (JP, A) JP 60-229733 (JP, A) JP 61 -108531 (JP, A) JP 62-113530 (JP, A) JP 63 51124 (JP, A) JitsuHiraku Akira 52-51367 (JP, U) JitsuHiraku Akira 64-30219 (JP, U) patent 2627040 (JP, B2) (58 ) investigated the field (Int.Cl. ^7, DB name ) B29C 55/00-55/30 B29C 47/00-47/96

Claims (5)

(57) [Claims] 1. Polyethylene, radical polymerization with ethylene
Copolymers of reactive monomers, polypropylene or their
A low melt tension thermoplastic resin consisting of a mixture is
The temperature is 40 ° C. above the melting point of the thermoplastic resin, and
Adjust to a temperature range 120 ° C higher than the melting point, and air at the base.
Equipped with an intake and an air outlet at the top, the diameter of the internal stabilizer
/ A small amount of air is continuously flowed between the internal stabilizer having a die diameter ratio of 0.7 to 1.0 and the molten resin bubble to bring the molten resin bubble into a non-contact state with the internal stabilizer. While supporting, the molten resin bubble is cooled while blowing cooling air in a bubble taking direction from an air ring having a plurality of annular slits provided at a position where the molten resin bubble is rapidly expanded, and the molten resin at an air ring outlet is provided. Adjust the bubble temperature to a range between the crystallization temperature of the thermoplastic resin and a temperature 60 ° C. higher than the crystallization temperature of the resin, and adjust the expansion ratio.
(Bubble diameter after expansion / thinnest before rapid expansion
Bubble diameter) is 1.3 to 6.0,
Distance to the lost line is in the range of 400-2000mm
A method for forming an inflation film, which comprises: 2. The thermoplastic resin is a linear low-density polyethylene, the lip gap is 2.5 to 5.5 mm, the extruded resin temperature is 170 to 250 ° C., and the resin temperature at the air ring outlet is 120 to 180 ° C. The method for molding an inflation film according to claim 1, wherein the thickness of the produced film is 10 to 80 μm. 3. The inflation according to claim 1 or 2.
As a film forming equipment, extruders, circular die for inflation having a bubble inside stable body, the blown film molding apparatus for thermoplastic resin comprising comprises an air ring, empty base
Equipped with air intake and air outlet at the top, diameter of internal stabilizer / die
A device for continuously flowing a small amount of air so that the internal stabilizer having a diameter ratio of 0.7 to 1.0 and the molten resin bubble do not come into contact with each other, and a plurality of annular members at positions for rapidly expanding the molten resin bubble. An inflation film molding apparatus having a slit, and a single air ring that blows cooling air in the take-up direction of molten resin bubbles by the annular slit. 4. The blown film molding apparatus according to claim 3 , wherein a means for heating the surface of the molten resin bubble is provided between the die and the air ring. 5. A method according to claim 3 or <br/> other is an air ring with outlet for blowing a plurality of annular slits and backward even cooling air to blow the molten resin bubble pick cooling air in the direction according to 4 Blown film forming equipment.